/Engine/Source/Runtime/Experimental/Chaos/Public/Chaos/Character/CharacterGroundConstraint.h
The constraint requires a character body, which is fixed, but the ground body is optional and can be changed dynamically using SetGroundParticleProxy
void Init ( [FSingleParticlePhysicsProxy](API\Runtime\Chaos\PhysicsProxy\FSingleParticlePhysicsProxy) * InCharacterProxy )